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Question about superatmospheric mesas.

I'm working on a worldbuilding project right now for a roleplaying game I intend to run sometime. The most unique thing about this world is that due to the flow of a sort of telluric energy, the magnetic poles of the planet (around 19 degrees away from the rotational north and south poles, like Earth) have tumesced out into great mesas that protrude beyond the atmosphere, probably about 25000 meters above sea level. These mesas are pockmarked with craters like the surface of the moon, and since the atmospheric pressure decreases by 1/2 every 5000 meters the atmosphere on the top is about 1/32 as thick as it is at sea level. Perhaps there is a little bit of lichen, but not much else can live there.

I wonder if you guys could help me back up a few assumptions I've made about how this would affect the climate and geology of the world.

-I'm thinking that cold air would be rushing downhill from the top of the mesa in a constant turbulent wind, creating persistent glaciation on the slopes that carves them into jagged mountain ranges. On the side of the mesas adjacent to the rotational poles, the glaciers would merge into the polar icecaps.

-Especially if the mesa was adjacent to a large ocean (like the northern one), the cold air coming down off the mountain and the warm air blowing in from the sea would create frequent and terrible storms, so that the mesa itself is usually obscured when viewed from sea level.

-The constant wind coming off of the mesa, the cold temperature and the moisture from the ocean would create a harsh, dense landscape- like Chilean Patagonia- in the land between the mesa and the ocean.

-The civilization that the players come from is itself not close to either of the mesas, and although naval expeditions have charted the coastline, the mesa was either obscured by storm or taken for a large chain of mountains.

-The other mesa is in the center of a large continent and is surrounded by high antarctic steppeland, populated thinly by hardy nomadic tribes. Although it is in a drier climate it too is ringed by glaciers and jagged mountains. It is also unknown to the European-analogue civilizations, although maybe the players could get some advice for how to survive in vacuum by talking with Uhrloni elders.

Does all this sound plausible to you guys? Could a 16th or 17th-century European civilization really be unaware of the existence of these things?

I've got a few sketches for maps, but no scanner and as yet no full-page world map. I'll try to get that done soon so I can show you what I'm talking about.

Edit: If this is in the wrong forum, I apologize; all the other threads seem to have maps attached

In the 16th and 17th century there were many white spots on the maps (especially around Antarctica). On the other hand: 25000 meter high mountains are visible from very far away, but they may be mistaken for lower mountains that are closer.
The physicist in me wants to know from what material these mesas are formed. Granite on an earthlike planet can reach up to 20000 meters (it can be calculated using only the melting enthalpy and the local gravity) and that is without erosion grinding it down. My best guess would be pure diamond (not sure about melting enthalpy but it should withstand erosion quite well)...

In the 16th and 17th century there were many white spots on the maps (especially around Antarctica). On the other hand: 25000 meter high mountains are visible from very far away, but they may be mistaken for lower mountains that are closer.

On an Earth-sized planet, you'd be able to see a 25km high mountain (or it'd be above the horizon, at least) for about 550km, or about 5 degrees; that's only up to (at most) the Arctic circle, which is a pretty high latitude. If the longitude of the pole was a long way from the European analogue, it's quite feasible that it wouldn't even have been noticed by them until the early modern era -- think something like the European exploration of Alaska or eastern Siberia, which weren't until the late sixteenth or early seventeenth century.
Of course, unless the coast was completely uninhabitable, there might be some human settlement -- though some parts of our own Arctic weren't settled until close to the modern era.

The mesas are not being held up by their own structure - they would collapse/ sink into the mantle really soon if that were the case. They're being held up by a constant welling up of energy along the magnetic poles of the planet. Although the planet has a floating crust, the mesas are thick cratons that have been fixed to the magnetic poles for billions of years (since the formation of the planet). They may rotate a bit over time as the land moves around them, but they probably contain some material that attracts to the very strong telluric (bull**** word but it'll do) field at those points. The magnetic poles do not wander nearly as much as those on Earth, although the polarity switches a few times per million years - with temporary catastrophic results.

I want the coastline of the Patagonia-like region bordering the northern mesa to have been charted by Thurian explorers, but I don't want them to have realized that the adjoining mountain range is actually five times as high as a regular one. Do you think it would be possible that the continual glaciation has carved away the slopes of the mesa enough that the curvature of the world prevents a traveller at sea level from truly seeing the unbroken limb of the central plateau on the horizon, instead seeing a jagged, glaciated mountain range?

-I'm thinking that cold air would be rushing downhill from the top of the mesa in a constant turbulent wind, creating persistent glaciation on the slopes that carves them into jagged mountain ranges. On the side of the mesas adjacent to the rotational poles, the glaciers would merge into the polar icecaps.

This assumption doesn't ring true to me. Of course, i don't know for sure, but let's think about this:
A) There's not very much atmosphere up there, so there's not that much air to rush down.
B) Since it's in proximity to stone, the air on top is likely to be warmer than if these mesas were absent, since the stone will store and reflect some of the solar radiation back into the air.

So i'd expect the local air-flow to be towards the mesa, at least at the edges, since the mesa warms the air, which then rises, creating a vacuum, etc. But this thing is so high, that i don't know if this would produce much of an effect on weather perceptible on the surface. I would treat them as walls for purposes of figuring prevailing winds and so forth.

I would also expect very little precipitation, or accumulation of ice and snow on the top (except perhaps in more or less permanent shadow). Evaporation happens more readily as air pressure decreases. Snow and Ice may also "sublimate", i.e. go directly from solid to gas.

High clouds in polar regions (according to wikipedia) have a hight of 3,000 to 8,000 m. If clouds don't come 1/3rd of the way up these monsters, i expect very little moisture on top.

Originally Posted by Turnpikelad

-Especially if the mesa was adjacent to a large ocean (like the northern one), the cold air coming down off the mountain and the warm air blowing in from the sea would create frequent and terrible storms,

Storms seem probable one way or another.

As to the question weather "civilization" could be unaware of these things-- I don't think they could be taken for "short" mountains unless explorers spend only a brief time on the mesa's coast. Sure clouds could hide them some of the time, maybe even most of the time, but always? I'd expect a break in the clouds sometime. These are so dramatically bigger than regular mountains, that if by no other means, the large shadow they cast should give them away. Of course it all depends on how wide these things are, and how far away the coast is from the lip. You describe them as "mesas" so i'm assuming they are generally pretty steep. But if the top is thousands of kms from the coast, nobody might see them.

Also something this big might have a noticeable effect on gravity. I don't know enough to tell you what that might be.

I would also expect very little precipitation, or accumulation of ice and snow on the top (except perhaps in more or less permanent shadow). Evaporation happens more readily as air pressure decreases. Snow and Ice may also "sublimate", i.e. go directly from solid to gas.

You're right about sublimation and evaporation. I only need these things to be high enough so that they're mainly bare rock, there is hardly any erosion (so that they can be essentially lunar terrain, scarred with billions of years of craters) and the air is effectively vacuum.

The glaciers should ideally go up most of the way to the top of the mesa... Imagine the Andes mountains, rising from a coastal plain, except as you go further inland the mountains keep getting higher and higher, the air thinner and thinner, until the glaciers fall away, and as you climb the last thousand meters (with breathing and pressure gear) the terrain flattens out until you are on a giant cratered plateau. I only need the plateau to be high enough that whatever glaciers there are have petered out, high enough that sublimation keeps the rock clear at the top. I chose 25000 meters because the 1/32 figure seemed close enough to vacuum, but maybe I only need 1/4 or 1/8 of sea level pressure to achieve this effect.